This paper reviews different methods to characterize the barrier and the micro-mechanical properties of polymer substrates coated with ultra-thin silicon oxide layers deposited by plasma process (PECVD). Uniaxial fragmentation tests are used to determine the evolution of oxygen barrier (OTR) of the barrier film under strain; this test method provides also the cohesive properties of the coating and the interfacial adhesion between the coating and the substrate. OTR evolution with strain has been demonstrated to be useful if a general knowledge is required on several samples, for example, as quality control tool, or for ranking crack onset strain (COS) of different sample types, but it does not provide any information on mechanical parameters such as the cohesion and the interfacial shear strength of thin coatings. These coating characteristics could be obtained by observation of the evolution of fragmentation patterns of coatings under uniaxial load by in-situ atomic force microscopy (AFM) or in-situ scanning electron microscopy (SEM). Considering its higher potential resolution and ease of operation, AFM fragmentation test should be preferred when a more precise knowledge of the micro-mechanical properties of the coated polymer films and of the coating surface behavior is needed. (C) Koninklijke Brill NV, Leiden, 2011